Typicallly kinder, gentler socieities get wiped militarily. Societies that focus more on militarization and toughness last longer. Societies that devote themselves to art and culture are usually vulnerable to invasion.

The way the system of government here is designed makes it increasingly difficult for one person to do that. That's what the founding "fathers" wanted to guard against when they accorded numerous powers to the legislature and judiciary. You also have the media which behaves like a fourth branch of government, in that their role is to impart journalism that puts a check on one man rule or fact fudging.